Many interfaces on aircraft structures and other types of structure may be sealed from various environmental elements, such as water, to keep these elements from penetrating through these interfaces and, in some cases, to ensure containment of the internal environment. One example of such interface is an interface between a fastener (e.g., a rivet) and aircraft skin. One area of concern is sealing fasteners inside wings, particularly wings that serve as fuel tanks Even small gaps may be of concern because a typical commercial aircraft may have thousands of rivets and other fasteners that are sealed. To cover gaps in these interfaces, various sealants may be used during or after installation of the fasteners. For example, a sealant may be deposited onto an internal surface of a skin at an interface area between formed by the skin and fastener. This application is typically performed using a handheld tool and involves manually aligning a dispensing nozzle with the fastener. Furthermore, to cover and fill the interface area with the material, a circular motion may be performed guiding the tip of the dispensing nozzle around the perimeter of the interface. For example, a portion of the fastener interfacing with a planar part may have a round shape defining a ring-shaped interface area. Maintaining the alignment is difficult during this circular motion and some material gets into the areas away from the interface. Furthermore, a similar circular motion may be performed to break the flow of the material. Specifically, a circular motion may be performed while retracting the application tool and separating the application tool from the applied material or, more specifically, in order to separate/break the application string of sealant from the dispensing nozzle. This circular motion is similar to the motion used to finish off application of soft ice cream into an ice cream cone. This application generally results in the fastener being fully covered with the sealant and not just the interface area. There are a few concerning issues with this approach.
The manual alignment and circular motions performed during application of a sealant take a significant amount of time. This time can be very extensive when viewed in light of the many thousands of fasteners that are being sealed on the same aircraft. This time results in added cost. Furthermore, the use of a handheld tool results more sealant than necessary being deposited to cover the interfaces. This excess is costly from the material consumption perspective. It also adds excessive weight to the resulting assembly often as much as 20-50 pounds for the same aircraft for the sealed fasteners. In some cases, the handheld tool and even robotic tools may be difficult to align with the rest to the sealing area and some gaps may remain exposed even when excessive amounts of sealant are deposited. Finally, fasteners that are not properly sealed may be reworked, which adds considerable time and cost to the manufacturing process.